Q: What is the value of Avogadro's number, and what does it represent?

$$6.02 \times 10$$^{23}$$, the number of atoms or molecules in one mole of a substance

Q: How many molecules are present in 2.00 moles of water ($$H_2O$$)?

$$1.20 \times 10$$^{24}$$ molecules

Q: Which formula would you use to convert the number of particles to moles?

$$\text{moles} = \dfrac{\text{number of particles}}{6.02 \times 10$$^{23}$$}$$

Q: How many atoms are present in 3.00 moles of aluminum ($$Al$$)?

$$1.81 \times 10$$^{24}$$ atoms

Question 1

What is the value of Avogadro's number, and what does it represent?

Accepted Answer

$$6.02 	imes 10$$^{23}$$, the number of atoms or molecules in one mole of a substance

Question 2

Which of the following best describes how to determine the mass of Avogadro's number of atoms for any element?

Accepted Answer

Use the atomic mass from the periodic table, expressed in grams, to find the mass of one mole (Avogadro's number) of atoms.

Question 3

How many molecules are present in 2.00 moles of water ($$H_2O$$)?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ molecules

Question 4

A sample contains $$3.01 	imes 10$$^{23}$$ atoms of sodium (Na$). What is the amount of sodium in moles?

Accepted Answer

0.500 moles

Question 5

What is the molar mass of $$CO_2 ($$carbon dioxide)?

Accepted Answer

$$44.0\ g/mol$$

Question 6

How many grams are in 0.25 moles of $$NaCl ($$sodium chloride)? (Molar mass of $$NaCl = 58.5\ g/mol)$$

Accepted Answer

$$14.6\ g$$

Question 7

Which formula would you use to convert the number of particles to moles?

Accepted Answer

$$	ext{moles} = \dfrac{	ext{number of particles}}{6.02 	imes 10$$^{23}$$}$$

Question 8

A compound has the empirical formula $$CH_2O$$ and a molar mass of $$180\ g/mol. $$What is its molecular formula?

Accepted Answer

$$C_6H_{12}O_6$

Question 9

Given a compound with 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass, what is its empirical formula?

Accepted Answer

$$CH_2O$$

Question 10

If you have 18.0 g of water ($$H_2O$$), how many moles of water do you have? (Molar mass of $$H_2O = 18.0\ g/mol)$$

Accepted Answer

1.00 mole

Question 11

Which of the following best describes the process for determining the percent composition of an element in a compound?

Accepted Answer

Divide the mass of the element in one mole of the compound by the molar mass of the compound, then multiply by 100%.

Question 12

A sample of glucose ($$C_6H_{12}O_6$) contains 3.01$$ 	imes $$10^{23}$$ molecules. What is the mass of this sample? (Molar mass of glucose = $$180\ g/mol)$$

Accepted Answer

$$15.0\ g$$

Question 13

Which of the following is the correct method to determine the molecular formula of a compound from its empirical formula and molar mass?

Accepted Answer

Divide the molar mass by the empirical formula mass, then multiply the subscripts in the empirical formula by this ratio.

Question 14

A compound contains 24.0 g of carbon, 4.0 g of hydrogen, and 32.0 g of oxygen. What is the empirical formula?

Accepted Answer

$$CH_2O$$

Question 15

Which of the following statements about the mole is correct?

Accepted Answer

A mole is the amount of substance that contains as many entities as there are atoms in exactly 12 grams of carbon-12.

Question 16

If a compound has a molar mass of $$34.0\ g/mol$$ and an empirical formula of $$H_2O$$, what is its molecular formula?

Accepted Answer

$$H_2O_2$$

Question 17

How many atoms are present in 3.00 moles of aluminum ($$Al$$)?

Accepted Answer

$$1.81 	imes 10$$^{24}$$ atoms

Question 18

A chemist needs 0.10 moles of $$CaCl_2$$ for an experiment. What mass of $$CaCl_2$$ should be weighed out? (Molar mass of $$CaCl_2 = 111$$\ g/mol$$)

Accepted Answer

$$11.1\ g$$

Question 19

Which of the following best explains why the empirical formula and molecular formula of a compound can be different?

Accepted Answer

The molecular formula is a whole-number multiple of the empirical formula, representing the actual number of atoms in a molecule.

Chapter 8: Quantities in Chemical Reactions – Study Guide and Learning Objectives

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